1. Field of the Invention
The present invention relates to a structure for fixing an electronic device having a heat-releasing plate to a substrate.
2. Related Art Statement
A fitting structure adapted to fixing an electronic device having a heat-releasing plate, e.g., a power transistor, to a substrate is heretofore known (For example, see JP-A 2003-318579 (pages 2 to 3 and FIG. 1).
A front face of the substrate is provided with a land portion to which a heat-releasing plate of the electronic device is to be soldered. A plurality of through-holes is provided to penetrate the substrate and the land portion for promoting release of heat from the electronic device. By this construction, heat generated in the electronic device can be released to the back face side of the substrate through the heat-releasing plate and the through-holes.
When the electronic device is to be fixed to the substrate, the device is arranged on a paste solder preliminarily applied to the land portion such that the heat-releasing plate may contact the solder, and the heat-releasing plate is soldered to the land portion by heating the substrate and temporarily melting the solder.
When the solder is melted in soldering the heat-releasing plate to the land portion, the electronic device descends toward the front face of the substrate due to its self weight. Consequently, the melted solder partially flows into the through-hole(s), the melted solder also partially runs out of an edge portion of the heat-releasing plate. Whether the heat-releasing plate has been well soldered to the land portion or not is judged by checking whether a run-out amount of the solder running out from the specific edge portion of the heat-releasing plate is not less than a prescribed amount or not.
However, the solder, which should have run out from the specific edge portion of the heat-releasing plate on soldering the heat-releasing plate to the land portion, sometimes partially flows into the through-hole(s). Consequently, a run-out amount of the solder from the specific edge portion of the heat-releasing plate is smaller than the prescribed one. Thus, even if the heat-releasing plate is appropriately soldered to the land portion, it may be judged on inspection that the heat-releasing plate is poorly soldered to the land portion.